Plasticizers are incorporated into a resin (usually a plastic or elastomer) to increase the flexibility, workability, or distensibility of the resin. The largest use of plasticizers is in the production of “plasticized” or flexible polyvinyl chloride (PVC) products. Typical uses of plasticized PVC include films, sheets, tubing, coated fabrics, wire and cable insulation and jacketing, toys, flooring materials such as vinyl sheet flooring or vinyl floor tiles, adhesives, sealants, inks, and medical products such as blood bags and tubing, and the like.
Other polymer systems that use of plasticizers include polyvinyl butyral, acrylic polymers, poly(vinylidene chloride), nylon, polyolefins, polyurethanes, silicon modified polymers, polysulphides and certain fluoroplastics. Plasticizers can also be used with rubber (although often these materials fall under the definition of extenders for rubber rather than plasticizers). A listing of the major plasticizers can be found in publications too numerous to mention.
Although the principal plasticizer for PVC are esters of phthalic acid (or the anhydride), recently there as been an effort to decrease the use of phthalate esters, particularly in end uses where the product contacts food, such as bottle cap liners and sealants, films, or for medical applications such as examination gloves, films, blood bags, and IV delivery systems, flexible tubing, or for toys, and the like. For these and most other uses of plasticized polymer systems, however, a successful substitute for phthalate esters has heretofore not materialized.
One such suggested substitute for phthalates are esters based on cyclohexane diacid esters. In the late 1990's and early 2000's, various compositions based on cyclohexanoate, cyclohexanedioates, and cyclohexanepolyacid esters were said to be useful for a range of goods from semi-rigid to highly flexible materials. See, for instance, WO 99/32427, WO 2004/046078, WO 2003/029339, U.S. Application No. 2006/0247461, and U.S. Pat. No. 7,297,738.
Other suggested substitutes include esters based on benzoic acid (see, for instance, U.S. Pat. No. 6,740,254, and also co-pending, commonly-assigned, U.S. App. Ser. No. 61/040,480 and polyketones, such as described in U.S. Pat. No. 6,777,514; and also co-pending, commonly-assigned, U.S. application Ser. No. 12/058,397. Epoxidized soybean oil, which has much longer alkyl groups (C16 to C18) has been tried as a plasticizer, but is generally used as a PVC stabilizer. Stabilizers are used in much lower concentrations than plasticizers. Esters based on glycerol are also a promising plasticizer for PVC and other polymer systems; see U.S. App. Ser. No. 61/040,490 and U.S. App. Ser. No. 61/040,480.
Di-2-ethyl-hexylterephthalate (DEHTP), sometimes referred to as Dioctylterephthalate (DOTP) has been described in the literature as a suitable candidate for a plasticizer since at least 1973.
U.S. Pat. Application 2005/0020718 teaches that esters of cyclohexane carboxylic acid esters may be used with terephthalates in PVC compositions. Among the specific terephthalates which are taught to be useful in combination with cyclohexane carboxylic acid ester include the alkyl terephthalates such as monomethyl terephthalate, dimethyl terephthalate, diethyl terephthalate, di-n-propyl terephthalate, di-n-butyl terephthalate, di-tert-butyl terephthalate, diisobutyl terephthalate, monoglycol esters of terephthalic acid, diglycol esters of terephthalic acid, di-n-octyl terephthalate, diisooctyl terephthalate, mono-2-ethylhexyl terephthalate, di-2-ethylhexyl terephthalate, di-n-nonyl terephthalate, diisononyl terephthalate, di-n-decyl terephthalate, di-n-undecyl terephthalate, diisodecyl terephthalate, diisododecyl terephthalate, di-n-octadecyl terephthalate, diisooctadecyl terephthalate, di-n-eicosyl terephthalate, monocyclohexyl terephthalate and or dicyclohexyl terephthalate.
A number of patents teach the use of terephthalate esters having low carbon numbers in the alcohol moieties, e.g., C4-C5 alcohols, in compositions with PVC, such as U.S. Pat. No. 7,361,779, and U.S. Pat. Application 2007/0037926.
U.S. Pat. Application 2008/0053863 discusses mixtures of C4-C8 terephthalates with butyls, acrylics, urethanes, polysulphides, and silicone modified polymers.
Other background references include EP 1 808 457 A, U.S. Pat. Nos. 3,736,348, 3,929,867, U.S. Patent Application 2007/027242, and WO 2008/140177.
The present inventors have surprisingly discovered that terephthalic dicarboxylic acid diesters synthesized with one or more of C5-C7 alcohols, particularly lightly branched C5-C7 alcohols, offer certain improved properties in compositions with PVC.